A cost of a solar cell per light-concentration area may be reduced by a combination of the solar cell and a cheap light concentrator. The light concentrator is one of optical elements. A device in which the light concentrator and the solar cell are combined is called a light-collecting type solar cell. Further, given the restriction of installation space and weight, the light concentrator is desirably as thin as possible.
As a technology that realizes the above, there is a light concentrator called Refraction (R), refleXtion (X), and total Internal reflection (I) (RXI) type light concentrator. This light concentrator has a characteristic of being extremely thinner than a conventional compound parabolic concentrator (CPC) type light concentrator.
The above light concentrator has been described about a solar cell. However, a lighting emitting diode (LED) is arranged in a place where the solar cell is arranged, and the device can be used as an LED illumination collimator lens. This is realized by reversibility of rays (the device is established if the ray direction is reversed). That is, the solar cell is replaced with the LED, and the ray direction is reversed, similar discussion to the case of the solar cell can be made. Therefore, hereinafter, the solar cell and the LED are called connection elements to be connected to the optical element (the light concentrator or the collimator lens). Further, a device in which the out element and the connection element are combined is called non-imaging type optical device.